Metalworking lubricant compositions are widely used in the steel and aluminum industries for reducing the thickness of sheet metal in rolling mills. The lubricant compositions are typically mineral oil or synthetic oil combined with various additives. Alternatively, they may be emulsions wherein a small quantity of oil is mixed with a larger volume of water. The compositions lubricate interfaces between rolls and sheet metal, and they cool the metal as it passes between sets of opposed rolls. After prolonged use, the lubricant compositions become contaminated with finely divided metal particles, metal oxide particles and other extraneous matter such as dirt. These contaminants decrease process efficiency, increase viscosity, reduce the activity of oil as a lubricant, and eventually cause smudging and other surface defects in the product.
When the lubricant composition is contaminated, its usefulness is reduced because the solid particulate contaminants furnish an undesired abrasive and because the particles increase viscosity of the oil phase. Accordingly, it is desirable to remove the solid particles so that oil in the composition can be reused.
In both ferrous and non-ferrous metalworking operations, filtration systems are customarily established for reclaiming hydrocarbon oils from used lubricants. In these systems, the oil is separated from water, if required, and then the oil is filtered through a particulate filter medium. Diatomaceous earth particles having an average size in the range of about 1-30 microns are widely used. Diatomaceous earth filtration prolongs the life of the filter cycle by preventing the filter cake from being blinded quickly by small particulates in the oil.
In the prior art, used diatomaceous earth was typically discarded after being used to filter lubricant oils. However, the discarded diatomaceous earth poses a potential environmental hazard because of its residual oil content. Accordingly, there is a need for a process capable of reclaiming residual oil from used lubricant compositions, without discarding a large volume of oil together with the filter medium.
Lubricant compositions employed in aluminum rolling mills generally contain mineral or synthetic oil together with various oil additives. These additives are generally organic compounds such as carboxylic acids, alcohols, and esters. One important feature of the present invention is that the process described herein recovers oil additives together with mineral oil or synthetic oil.
A principal objective of our invention is to provide an economical process for removing solid particles from lubricant compositions.
A related objective of our invention is to provide a process for removing solid particles from lubricant compositions without adding any organic solvents such as benzene, toluene, methanol and tetrahydrofuran. These solvents pose serious health risks to persons inhaling or ingesting them, and they are potentially hazardous to the environment.
Additional objectives and advantages of our invention will become apparent to persons skilled in the art from the following detailed description.